There are some known circular knitting machines which are fitted with a certain number of vertical needles mounted on a cylinder and a number of horizontal needles mounted on a dial placed on top of and revolving with said cylinder to allow a co-operation of the vertical and horizontal needles in knitting ribbed fabrics according to a given selection, perforated fabrics, paterned or plain fabrics, by transferring meshes from horizontal to vertical needles or by excluding said horizontal needles from operation.
In said known machines the dial bearing the horizontal needles is fitted with a stationary cover equipped with cam means to control the radial reciprocating displacements of horizontal needles and to guide said needles along an inactivating track.
In some embodiments the horizontal needles on one half of the dial have butts which are higher than the butts of the needles on the other half of the dial. In this case ribbed fabrics can only be made using all the needles on the dial plate and then, if necessary, at least half of the dial needles may be selected to transfer their meshes to the vertical cylinder needles as is usually done at the beginning of of heel and sole of a stocking.
In some other embodiments the dial plate is provided with more than two rows of horizontal needles, the needle butt height being different in each needle row. The availability of needles with butts of different heights increases the selectivity of said needles to produce differently ribbed or perforated fabrics as well as other patterns and also allows the selection of the needles designed for the transfer of meshes to the vertical cylinder needles. At any rate, selection of horizontal needles on the dial plate is so far obtained by either fixed or movable cam devices fitted to the stationary cover and acting only on the butts of said needles.
A system of this kind implies however some difficulties and both practical and functional limitations, as the height difference between butts of several needle rows cannot be too great, as otherwise the space required by the dial plate would be too large. In addition, the control cams acting on the higher butts might bend or warp said butts and thus cause needle jamming or an inaccurate selection.
If several needle rows with butts having different height are used, the needles with butts of the same height can only be selected all together and in the same way according to a fixed and unchangeable selection, it being impossible to select only some needles out of a row, thus preventing the production of different patterns as is often desirable and required.
The dial plate with horizontal needles is normally also equipped with a thread saw which generally projects from the dial plate circumference at least as much as its teeth are long. At any rate, the teeth of said saw must be within the circumference on which the vertical cylinder needles are placed and the dial plate diameter must therefore be comprised within certain limits. On the other hand, by restricting the diameter of the dial plate its supporting and guiding possibilities will also be reduced, in particular when its horizontal needles are taken to the outside and thus overhang by a large amount.